The present invention relates to a toner composition for electrophotography, and more particularly to an electrophotographic toner composition having excellent blocking resistance and offset resistance which contains a rosin type polymeric compound as a binder.
Various electrophotographic methods are hitherto known. There is generally known a method in which a latent electrostatic image is formed on a photosensitive body utilizing a photoconductive material by various means and is then developed with a toner, and after transferring the toner image to a support such as paper if necessary, the toner image is fixed by heating, applying a pressure or using a solvent.
In recent years, a high speed fixing property is required for the toner in order to increase the efficiency of the copying operation. Attempts such as using a thermoplastic resin having a lower softening point and being easily heat fusible as a toner binder to be used in a conventional heat fixing method have been made to provide a toner composition satisfying the requirement. However, mere lowering of the softening point of a resin binder has the defect of causing agglomeration of toner particles, namely blocking phenomenon, during use. Accordingly, as one system for high speed fixing, there has been utilized a fixing method using a heat roller having a good heat conductivity.
Since the heat roller system is higher in heat efficiency than the heat fixing system, a toner can be fixed in a shortened period of time. However, sticking of the toner to the heat roller, namely the so-called offset phenomenon, frequently occurs, since the toner is directly brought into contact with the heat roller. Accordingly, it has been desired to develop a resin capable of solving this problem.
A styrene-acrylate copolymer, a styrene-butadiene copolymer and a styrene-acrylonitrile copolymer are usually known as a resin binder for a toner. These vinyl copolymers are in general poor in offset resistance and flowability. One of other resin binders is a bisphenol type epoxy resin. The bisphenol type epoxy resin provides a toner having superior flowability and fixing property because of having a lower molecular weight as compared with the vinyl copolymer binder. But, it has a tendency to lowering the offset resistance, because the melt viscosity of the resin is low. Also, various polyester resins are proposed as toner binders having excellent offset resistance and flowability.
It is an object of the present invention to provide a novel resin binder for a toner used in electrophotography having excellent blocking resistance, offset resistance and low temperature flowability.
A further object of the invention is to provide an electrophotographic toner composition having excellent blocking resistance, offset resistance and low temperature flowability.
These and other objects of the present invention will become apparent from the description hereinafter.